Beyond the bulk: probing the EUV optical constants of nanoscale amorphous silicon films

This study investigates the optical constants of amorphous silicon (a-Si) thin films, deposited using direct current (DC) magnetron sputtering technique with varying thicknesses (5 nm to 50 nm), in the extreme ultraviolet (EUV) range using monochromatized synchrotron radiation. In addition to EUV reflectometry, complementary characterization techniques, including X-ray reflectometry (XRR) and transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDX), were employed to evaluate the film thickness, interface quality, and elemental composition. Variations in optical behavior were observed with changing thicknesses. Additionally, a notable deviation in the reconstructed optical constants at the Si L₂, ₃ absorption edges was identified. This new experimental dataset on the optical constants of a-Si significantly expands the existing literature data, particularly in the near-edge regions, and enhances our understanding of the optical properties of a-Si thin films.